EP-2016-280

(Submitted on 18 Nov 2016)

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Abstract

Measurements of charm mixing and $C\!P$ violation parameters from the
decay-time-dependent ratio of $ D^0 \to K^+ \pi^- $ to $ D^0 \to K^- \pi^+ $
decay rates and the charge-conjugate ratio are reported. The analysis uses
$\overline{B}\to D^{*+} \mu^- X$, and charge-conjugate decays, where $D^{*+}\to
D^0 \pi^+$, and $D^0\to K^{\mp} \pi^{\pm}$. The $pp$ collision data are
recorded by the LHCb experiment at center-of-mass energies $\sqrt{s}$ = 7 and 8
TeV, corresponding to an integrated luminosity of 3 fb$^{-1}$. The data are
analyzed under three hypotheses: (i) mixing assuming $C\!P$ symmetry, (ii)
mixing assuming no direct $C\!P$ violation in the Cabibbo-favored or doubly
Cabibbo-suppressed decay amplitudes, and (iii) mixing allowing either direct
$C\!P$ violation and/or $C\!P$ violation in the superpositions of flavor
eigenstates defining the mass eigenstates. The data are also combined with
those from a previous LHCb study of $D^0\to K \pi$ decays from a disjoint set
of $ D^{*+} $ candidates produced directly in $pp$ collisions. In all cases,
the data are consistent with the hypothesis of $C\!P$ symmetry.

Efficiency corrected and SS background subtracted
ratios of WS/RS decays
and fit projections for the DT sample.
The top plot shows the $ D ^0$ $(R^+(t))$ sample.
The middle plot shows the $\overline{ D }{} {}^0$ $(R^-(t))$ sample.
The bottom plot shows the difference between the top
and middle plots.
In all cases, the error bars superposed on the data
points are those from the $ \chi^2 $ minimization fits
with no accounting for additional systematic
uncertainties.
The projections shown are for fits assuming $ C\!P$ symmetry (solid blue line),
allowing no direct $CPV$ (dashed-dotted green line), and allowing all forms of $CPV$ (dashed magenta line).
Bins are centered at the average value of $t/\tau$
of the bin.

Efficiency-corrected data
and fit projections for the DT (red open circles) and prompt (black filled circles) samples.
The top plot shows the $ D ^0$ $(R^+(t))$ samples.
The middle plot shows the $\overline{ D }{} {}^0$ $(R^-(t))$ samples.
The bottom plot shows the difference between the top
and middle plots.
In all cases, the error bars superposed on the data
points are those from the $ \chi^2 $ minimization fits
without accounting for additional systematic
uncertainties.
The projections shown are for fits assuming $ C\!P$ symmetry (solid blue line),
allowing no direct $CPV$ (dashed-dotted green line), and allowing all forms of $CPV$ (dashed magenta line). Bins are centered
at the average $t/\tau$ of the bin.

This ZIP file contains supplemetary material for the publication
LHCb-PAPER-2016-033. The files are:
supplementary.pdf : An overview of the extra figures
*.pdf, *.png, *.eps : The figures in various formats